Corrosion inhibition



been mentioned above.

1 j CQRROSION'INHEBITION Kenkere 1. 'Channabasappa, Chicago, 111., assignor to Wright Chemical Corporation, Chicagmlll.

:NoDrawing. Filed Feb. -18, 1950, Ser. No. 9,422

' 11 Ciaims. \(Cl. 252 -389) This invention relates to the inhibition of corrosion of metals which come into'contact with water as, for-example,

in water circulation systems, particularly industrial water systems such as utilize heat exchangers, cooling towers and like installations. While it is; especially concerned with ,the protection against corrosion of ferrous .metals such-as iron and steel, it is alsouseful for inhibiting corrosion of other metals in contact with water, particularly flowing a water, as, for example, copper, copper alloys such as brass ,andbronze, aluminumandaluminumbase.alloys,..couples a of such metals with ferrous metals, and other metals and alloys commonly-used in industrial water systems or Water circulation systems.

rosion inhibition of metals used in water systems where circulating watercomes into contact with such metal sur-v faces. Among the materials utilized. as additives to the water to effect corrosion inhibition of the aforesaid types of metals are water-soluble phosphates of variousitypes including monosodium-phosphate and sodium polyphos- United, States Patent 3,133,028 Patented May 12, 19:64

,. v ce 'cyanates, and/or water-soluble thiourea compounds of the type represented -by' the formula where R, R R and R are each selected from the group consistingof hydrogen, alkali metal, and alkyl radicals containing from 1 to 4.carbon atoms such as methyl, ethyl, propyl, .isopropyl, butyl'and isobutyl. It also has been found'that water-solublethiocarboxylic acids and salts 1 thereof can be utilized as, for example, thioglycolicacid, thiodiglycolicacid'and thiomalic acid and the ammonium and sodium salts thereof.

Among the water-soluble thiocyanates are thiocyanic acid and the inorganic salts of thiocyanic acid, particularlythealkali-metal thiocyanates, namely, sodium, potassium, ammoniumand lithium thiocyanates. Other watersoluble thiocyanate compounds which, in aqueous soluf .20 A greatdealof work has been done in-the 'fieldof' corphates; Water-soluble hexavalent chromium compounds such as sodinm and potassium chromates.anddichromates;

1 and various combinations of ingredients as, for instance,

mixtures of water-soluble trivalent and hexavalent chrov fe'rricyanides, and water-soluble chromates. Typical of 'such'a'pproaches are disclosedin US. Patents Nos. 2,793,- 93 2; 2,887,085 and 2,901,437. While improvement in corrosion inhibition is obtained by'following such and other practices of the priorart, nevertheless not infr e uently problems of scaling and pitting arise and, in addi- ..tion, the matter of cost of the' corrosion inhibiting compositions is a factor of material consideration.

The present invention is based upon discoveries which result in new and useful corrosion inhibition compositions andfsignificant improvements in regard to inhibition of corrosion of ferrous andother metals through the utilization of suchcompositions.

Ithas been discovered that the employment, in con- I junction with water-soluble hexavalent chromium compounds, of certain chemical compounds, hereafter ,de-

scribed, brings aboutmarked improvement in the corrosion inhibition properties of said hexavalent chromium compounds when dissolved in water and said water is in contact with or is circulated'in contact with ferrous metals and other metals in water systems such as have themselves particularly in regard to 'very substantially reduced scaling, which is'one of the serious objections, for

1 example, of theuse of polyphosphates and various other materials heretofore suggested 'as corrosion inhibiting materials, and in regard to substantial absence of pitting Another important advantage resides in the fact that the compounds; mixtures of certain fln'ols, water-soluble zinc compounds, and water-soluble polyphosphates; and mixtures of water-solublepolyphosphates, water-soluble urea compounds.

Ithas also been found to be particularly desirable to employ, in' conjunction with the water-soluble hexavalent chromium compound, one or more water-soluble zinc compounds, particularly zinc compounds such as zinc sulfate,zinc chloride, sodium 'zincate, and zinc oxide and 'zinc carbonate in acid solutions in which they are soluble.

Other water-solublezinc compounds which, in aqueous solution,ion-ize to produce zincions can be utilized. Where the zinc compounds are used, it will be understood that such-will -be selected, in relation to the hexavalent chromium compound or compounds and thiocyanate or thiourea compound, as to be compatible therewith.

With water-soluble hexavalent chromium compounds -are, -as' indicated above," well known in the art." They include, particularly the alkali'metal chromat'es and dichromates such as sodium'chromate, potassium dichromate, ammonium dichromate, and chromium trioxide in their anhydrous and hydrate forms. U l

The ranges "of concentration in the water of the ingredients utilized'pursuant to the presentinvention are quite variable. Thus; in the'case' of the hexavalent chromium compound; the concentration may range from about 1 to "10,000 ppm, better stillfrom 2to 100 p.p.m., and

particularly desirably from 5' to'30 p.p .m., all calculated These improvements manifest v invention makes possible the utilization of reduced concentrations of hexavalent chromium compounds, thereby resulting in savings in cost.

7 The chemical compounds which are used in conjunction i with the water-soluble hexavalent chromium compounds pursuant to the present invention are water-soluble thio- 5 asNa CrO In the case of the thiocyanates, the thiourea'c'oinpounds and the thiocarboxylic acid compounds,

the concentratio mayrange" from about 0:01 top.p.m., better still'from 0.0l1toi-25 ppm, and particularly desirably from 0.02 to 10 ppm. Inthe case of the zinc 'compounds,"'where the same are used, thewconcentration may'raiige from names to 25 p.p.m., better still from 0.5 to 15 p'.p.m.,-and particularly desirably from'l to 8 ppm. calculated as zinc.

It .will. be understood that, if desired,- supplemental ingredients can be added to the compositions of the present invention or to water containing the compositions of the invention, so long as the amounts-or character of such supplemental ingredients are not such as unduly ad'- versely affectthe desired properties of said compositions or water containing the" same. 'ThuS,'f0I"XamP1e,jtri* Mixvalent chromium compounds, phosphates and polyphosphates, and thiols can be added in relatively minor amounts. It is preferred, however, not to utilize said or other supplemental ingredients.

The following examples are illustrative of corrosion inhibiting compositions falling within the scope of the invention. It will be appreciated that other compositions can readily be prepared in the light of the guiding principles and teachings provided herein. All parts listed are by weight.

Example 10 Sodium dichromate 100 Chromic acid (as Cr O 65 Zinc sulfate 25 Ammonium thiocyanate 0.2

Example 11 Sodium dichromate '1 100 Chromic acid (as Cr O 20 Zinc sulfate 6 Thiourea 0.3

Example 1 The following table shows the unusual results and Ammonium dichromate 100 synergistic coaction of the ingredients in compositions Ammonium thiocyanate 0- made in accordance with the present invention.

RECIRCU LATIN G COOLING TOWER Duration of test, days 28 pH range 6.08.0 Chloride as NaCl '1O100O Total hardness 10-1000 Heat exchanger temperature F 70-400 Sulfate as Na2SO4 p.p.m. 10-1500 VI+ III+ II+ Water Corro- Test N0. Orion, Or ion, Zn ion, soluble Type of organic Type of Attack sion p.p.1n. p.p.m. ppm. phosphate, compound, p.p.m. rate,

p.p.m. MPY

20 Extensive pitting. 10 8 do 20 8 Moderate pitting 12 s d 7 3 do 7 8 Extensive pitting. 10 8 Some pitting 5 8 Sullonate, 1.- d 4 8 Citrate, 0.05 do 6 8 Ethylene diamine Moderate pitting 7 gegracetic acid, 8 2 Thi0 cyanate,0.02- Negligible 1 8 1 Thiourea, 0.02 do 1 8 Thiocyanate, 0.05... do 1 8 (Ortho) Some pittin 4 *Mils per year.

Example 2 40 It will be seen, from the foregoing table, that hexavalent Potassium dichromate 10o chromium alone in the amount of ppm. as hexavalent Onium thiocyanat; 02 chromium ion caused extensive pitting and showed a cor- Zinc Sulfate ""f'" rosion rate of 10 mils per year. Hexavalent chromium in admixture with trivalent chromium showed moderate Example 3 pitting and a corrosion rate in the range of 12 to 7 mils Potassium dichmmate 100 per year. Hexavalent chromium and zinc ions with and Thiourea 2 without certain supplemental agents showed from extensive to some pitting and a corrosion rate of from 10 to Example 4 .4 mils per year. In sharp contrast to the above, the Potassium dichrom 100 addition of as little as 0.02 to 0.05 ppm. of thiocyanate Thiourea 0.2 n is case sodium thiocyanate) or thiourea to 8 ppm. Zinc sulfate 40 f eXavalcnt chromium ion, with and without from 2 to E am [e 5 1 ppm. of zinc ion, showed no pitting and a corrosion x 17 rate of less than 1 mil per year. The coaction between Sodium dichromate 100 the hexavalent chromium and the thiocyanate or thiourea, Ammonium thiocyanat 5 in the presence as well as without the presence of the Thiourea zinc ion, demonstrates a highly surprising and effective S9d1um polyphosphate 10 'syllfilgistic-like action, Zinc ulfa 5 What is claimed as new and desired to be protected by Example 6 Letters'Patent of the United States is: 1. A corrosion inhibiting composition useful upon 100 fi g g z gg gzgg 0.2 v addition to water to lnhibit corrosion of ferrous metals m y n in contact with said water, said composition consisting Example 7 essentially of the following ingredients in substantially Ammonium dichromate 100 the following parts by weight in relation to each other: Ammomum thloglycolate A member selected from the group con- Example 8 sisting of water-soluble chromates Ammonium dichmmate 100 and dichromates 1 to 10,000 Ammonium thiomalate 0.3 (calculated as I i Na CIO Exam? 9 9 Water-soluble thiocyanate compound 0.01 to 100. Sodium dichromatc 100 Chromic acid (as Cr O 15.6 2. A corrosion m lbl ll'lg composition useful upon addl- Zinc oxide Q 6.5 tion to water to inhibit corrosion of ferrous metals in Ammonium thiocyanate 0.2 contact with said water, said composition consisting escalculated as zinc.

sentially of the following ingredients in substantially the following parts by weight in relation to each other:

A memberselected from the group consisting of Waterasoluhle chromates and 'dichro'mates 2 to 100 1 (calculated as Na CrO Water-soluble thiocyanate compountL- 0.01 to 25.

3. A composition in accordance with claim 2, including from 1 to '8 parts of a water-soluble zinc compound 4. A corrosion inhibiting composition useful upon addition to water to inhibit corrosion of ferrous metals in contact with said water, said composition consisting essentially of the following ingredients in substantially the following parts by Weight in relation to each other:

V A member selected from the group consisting of water-soluble chrornates and ;dichromates 1 m 10,000

' a (calculated as v V Na CrO A thiourea compound corresponding R\ E /R2 N o-N 12 R;

where R, R R and R are each selected from the group consisting of hydrogen, alkali metal, and alkyl" radicals containing from. 1 to 4 carbon atoms r 0.01 to 200.-

6. A composition in accordance with claim 4, including from 0.5 to 25 parts calculated as zinc.

- 6. A corrosion inhibiting composition useful upon addition to water to inhibit corrosion of ferrous metals in a contact with saidwater, said composition consisting essentially of the following ingredients in substantially the following parts by weight in relation to each other: i

V A member selected from the group consistingof water-s oluble chromates and dichromates 2 to 100 a (calculated as NfizCIO). I Thiourea -4. 0.01 to 25.

- '7.j'A corrosion inhibiting composition useful upon addition to water to inhibit corrosion of ferrous metals incontact with said Water, said composition consisting essentially of the following ingredients in substantially the following parts by weight in relation to each other:

A member selected from the group consisting of water-soluble chromates and dichromates 5 to 30 (calculated as g V Na CrO V Chomic aCid 5 to 30 Thiourea 0.02 to 10 8. A process of protecting ferrous metals against corrosion by water circulated in contact therewith, the step which consists essentially, in adding to the water the following ingredients in the stated concentration in ppm. basedon the water:

' calculated 7 Hex-avalent chromium as Na2CIO4 o Water-soluble thiocyanate compound---" 0.01 to 9. A process of protecting ferrous metals against corrosion by water circulated in contact therewith, the step which consists essentially in adding to the water the following ingredients in the stated concentrations inppm. based on the water: i

Hexavalent chromium calculated as Na CrO 1 to 10,000 Water-soluble zinc compound calculated as in zinc ion 0.5 to 20 Ammonium thiocyanate a 0.01 to 200 10. The method of retarding the corrosion of a ferrous metal upon contact with water which comprises effecting such contact in the presence of a Water-soluble corrosion inhibitor dissolved in said water, said inhibitor consisting essentially of a 'water-soluble hexavalent chromium compound, a water-soluble zinc compound, and a watersoluble thiocyanate, said ingredients being present in the water in the following amounts in terms of p.p.m.:

Hexayalent chromium compound (calculated as Na CrOQ- -l 5 to 30 Zinc compound (calculated as zinc ion) 1 to 8 Thiocyanate 0.02 to 10 11. The method of retarding the corrosion of a ferrous metal upon contact with water which comprises,

effecting such contact in the presence of a Water-soluble corrosion inhibitor dissolved in said water, said inhibitor consisting essentially of a water-soluble hexavalent chromium compound, "a water-soluble zinc compound, and thiourea, said ingredients being present in the Water in the following'anrounts in terms of p.p.m.: I

Hex-avalent chromium compound (calculated as Na CrO 5to 30 Zinc compound (calculated as zinc ion) lto 8' Thiourea r 0.02 to 10 References Cited in the file of this patent UNITED STATES PATENTS 

1. A CORROSION INHIBITING COMPOSITION USEFUL UPON ADDITION TO WATER TO INHIBIT CORROSION OF FERROUS METALS IN CONTACT WITH SAID WATER, SAID COMPOSITION CONSISTING ESSENTIALLY OF THE FOLLOWING INGREDIENTS IN SUBSTANTIALLY THE FOLLOWING PARTS BY WEIGHT IN RELATION TO EACH OTHER: 